The invention relates to a semiconductor detector for the detection of ionizing radiation (gamma rays, X-rays, etc.).
More particularly, the invention relates to a device for supplying the polarization voltage of the semiconductor detector for detection of ionizing radiation (gamma rays, X-rays, etc.).
The invention relates particularly to fields in which the detected radiation is high-energy radiation, for example such as astrophysics or nuclear medicine.
A semiconductor detector is in the form of a mosaic of elementary detectors, or pixels, assembled together to form at least one detector block.
Each detector pixel is composed of one semiconducting element, for example CdZnTe, placed between two armatures.
A detector pixel converts the energy in photons received by it into charge carriers. Charge carriers are collected using a polarization voltage applied to the armatures of the detector pixel.
Detector pixels are glued onto an electronic substrate that includes a polarization resistance, a coupling capacity and a load preamplifier. The signal is amplified and shaped by an electronic measurement circuit.
In order to more efficiently detect high-energy radiation, the semiconducting element located between the armatures of the detector pixels has to be thickened.
A higher polarization voltage is necessary to polarize a thicker semiconductor detector. The voltage can thus be as high as several hundred volts.
For example, the polarization voltage for the ISGRI (Integral Soft Gamma Ray Imager) imager onboard the INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory) satellite is typically equal to 200 V.
Polarization voltages for the PEGASE (Projet d""Etude de Gamma camxc3xa9ra A SEmiconducteurxe2x80x94study project for semiconductor gamma camera) are between 500 V and 1000 V.
The semiconductor detector for the ISGRI imager is described in the document entitled xe2x80x9cA Basic Component for ISGRI, the CdTe Gamma Camera on Board the INTEGRAL Satellitexe2x80x9d, M. Arques et al., published in xe2x80x9cPaper presented at Toronto 1998 IEEE NSS conferencexe2x80x9d.
A detector block for the ISGRI imager is shown in FIG. 1.
FIG. 1 shows a top view of a block of detector pixels according to the ISGRI imager. The block of detector pixels is composed of 16 detector pixels P assembled side by side to form a 4xc3x974 matrix. Each detector pixel P has an armature A on its top face. The complete set of armatures A with detector pixels P defines a detector plane exposed to the radiation to be detected.
The polarization voltage is brought to the armatures A using a wire F. The wire F is bent and glued to distribute the polarization voltage to the set of armatures A. Bending and gluing of wire F are difficult and expensive operations.
The polarization voltage originates from a power supply device external to the detector (not shown in the figure) through a current wire on the electronic substrate located at the back of the detector block. It is then necessary to pass the wire along the detector block in a direction approximately perpendicular to the detector plane. In order to avoid any false contact, the wire F is encased in a jacket G in the area in which it connects the back face and the front face of the detector block.
The jacket G is composed of an insulator with a thickness that increases as the voltage carried by the wire increases.
When several detector blocks are assembled side by side to form a unique detection assembly, the size of the jacket G on each detector block creates a dead non-detection area in the detector plane. This dead area in which there is no detection is larger when the polarization voltage is high. This is a disadvantage.
As mentioned above, the polarization voltage passes through the electronic substrate at the back of the detector block. The back face of the detector block is also the area in which useful signals originating from radiation detection and all electrical signals necessary for operation of the measurement electronics circuit, are present.
Thus, local precautions are necessary between the polarization voltage and other signals. These precautions become particularly difficult to achieve when the polarization voltage is high and when the useful signals are equal to, for example, a few Femtocoulombs. It is then necessary to keep the polarization voltage separate from the useful signals, which reduces the useful area of the electronic substrate located on the back. This reduction of the useful area may be such that it is impossible to design a circuit that operates reliably.
The document entitled xe2x80x9cRxc3xa9alisation et evaluation des performances d""une camera miniature pxc3xa9ropxc3xa9ratoire CDTExe2x80x94Manufacture of a CDTE miniature surgical camera and evaluation of its performancesxe2x80x9d, Bedoui H. et al., published in Innov. Tech. Biol. Med., vol. 19, No. 1, 1998, also discloses a semiconductor detector according to prior art. The detector pixels in this case are also grouped into detector blocks.
Each detector pixel of a detector block is individually polarized by a wire connected to the periphery of the detector plane. A dead area in which there is no detection then appears where the wires pass. Therefore, this solution limits the detection area and makes it impossible to make large detection areas. For example, it is impossible to make 200xc3x97200 mm2 detection areas like those envisaged for PEGASE.
The invention does not have the disadvantages mentioned above.
The invention relates to a semiconductor detector comprising at least one first detector block composed of elementary detector pixels assembled side by side on the same substrate, each elementary detector pixel being composed of a semiconducting element with a first face covered by a first armature and a second face covered by a second armature, the elementary detector pixels being assembled side by side such that the first armatures define a detector plane and the second armatures define an approximately plane surface in contact with the substrate. The first armatures are covered by a plane conducting structure that connects them together electrically.
One advantage of the invention is that it can be used to make a semiconductor detector with almost no non-detection area.